1. Field of the Invention
The present invention relates to an optical element.
2. Description of the Related Art
In an optical device such as a camera or the like, a diaphragm, a neutral density (ND) filter or the like is used in order to adjust an amount of light that enters into a lens or the like. Recently, a camera is mounted on a mobile phone, a mobile terminal or the like so that a diaphragm is used in such a camera (Patent Document 1, for example).
FIG. 1 illustrates a general diaphragm. A diaphragm 910 includes a tabular member made of a shading material and provided with an open portion 911 at a center portion. Thus, in the diaphragm 910, light is shaded at a peripheral portion and transmitted at the center portion where the open portion 911 is formed. In FIG. 1, (a) is a top view of the diaphragm 910 and (b) illustrates transmittance of light along a dashed line 1A-1B in (a).
Recently, the size of each camera is becoming smaller in accordance with a smaller size and a thinner size of each mobile phone or each mobile terminal. Thus, the size of each diaphragm is also becoming smaller. However, in the small-size diaphragm 910, generation of diffraction of light at the periphery of the open portion 911 cannot be ignored so that it is becoming difficult to increase resolution. This means that, a small-size diaphragm is required in which resolution is not deteriorated even with a camera with high-pixels.
[Patent Document]
    [Patent Document 1] Japanese Laid-open Patent Publication No. 2006-301221